The following discussion of the prior art is intended to present the invention in an appropriate technical context, and allows its significance to be properly appreciated. Unless clearly indicated to the contrary, reference to any prior art in this specification should not be construed as an expressed or implied admission that such art is widely known or forms part of common general knowledge in the field.
Vortioxetine (the Compound (I)), is a typical antidepressant indicated for the treatment of major depressive disorder and marketed under the brand name as TRINTELLIX. The marketed compound is in the form of its hydrobromide salt which is chemically known as 1-[2-(2,4-dimethyl-phenylsulfanyl)-phenyl]-piperazine, hydrobromide, and is structurally represented as follows;

Vortioxetine being an important antidepressant agent; a number of processes for its preparation as well as for its intermediates are known in the art.
U.S. Pat. No. 7,144,884 refers to the phenylsulfanyl-piperazine compounds, wherein generically as well as with analogous compounds, it describes a process for the synthesis of vortioxetine comprising the reaction of amine compound with an alkylating agent as depicted below; however the patent does not provide any specific reaction conditions:

U.S. Pat. No. 9,493,409 describes a process for the preparation of vortioxetine consisting of reacting 2-((2,4-dimethylphenyl)thio)aniline with bis(2-chloroethyl)amine hydrochloride in the presence of diethylene glycol methyl ether at 130° C. for 3 days to provide the product as vortioxetine hydrochloride as white powder with 53% yield.
Published PCT application WO 2016/004908 A1 describes a process for the preparation of 1-(2-(2,4-dimethylphenylsulphanyl)phenyl)piperazine comprising reaction of 2-(2,4-dimethylphenyl sulphanyl) benzeneamine with a suitable precursor of formation of piperazine ring in an aromatic solvent selected from the group consisting of chlorobenzene, xylene, toluene, α,α,α-trifluorotoluene and their mixtures, to provide product with overall 50% yield.
Chinese patent application CN 103788019 describes a process for the preparation of 1-(2-(2,4-dimethylphenylsulphanyl)phenyl)piperazine comprising cyclization reaction of 2-(2,4-dimethylphenylsulphanyl) benzeneamine with a suitable precursor as bis (2-haloethyl) amine; wherein the said cyclization reaction is carried out in the presence of an acid binding agent such as triethylamine, pyridine, N-methylmorpholine, diisopropylethylamine or 4-dimethylaminopyridine.
In addition to the afore discussed patent documents, there are a number of patent documents that describe a process for the preparation of vortioxetine, its intermediates and salts thereof. For instance, published PCT application WO2015114395 and WO2014161976A1; published US patent application 2016/0060215; Chinese patent applications CN 103788020, CN 103936694, CN 104109135, CN104098530; U.S. Pat. No. 9,095,588 B2 describes a process for the preparation of vortioxetine and its salts.
It is evident from the discussion of the processes for the preparation of vortioxetine and its salts, described in the afore cited patent documents that the reported processes provide a product with low yield and purity, which requires repeated purification or multiple crystallization steps. Also, the prior art process also refers the use of various reagents and coupling agents such as acid binding agent, metal catalyst or a phosphine ligand; which renders the process costlier and hence are not industrially feasible. In view of these drawbacks, there is a need to develop an industrially viable commercial process for the preparation of vortioxetine; which is a simple, efficient and cost-effective process and provides the desired compounds in improved yield and purity.
Inventors of the present invention have developed an improved process that addresses the problems associated with the processes reported in the prior art. The process of the present invention does not involve use of any toxic and/or costly solvents, also does not involve use of costlier coupling agents and reagents. Moreover, the process does not require repetitive purification steps. Accordingly, the present invention provides a process for the preparation of vortioxetine, which is simple, efficient, cost effective, environmentally friendly and commercially scalable for large scale operations.